An electronic device comprising two antennas connected to an electronic member, for example a chip, said electronic member being mounted on a support plate, is known from the prior art. Each antenna has a substantially helical shape. Each antenna comprises a steel core coated directly with a brass coating, brass being an alloy of copper and zinc in respective proportions of around 75% and 25%.
It is known that the electromagnetic conduction for such an antenna takes place mainly through the skin effect, that is to say electromagnetic conduction takes place mainly in the outer layers of the antenna. The skin depth depends especially on the frequency of the radiation and of the constituent material of the conduction layer. To give an example, for a UHF frequency (for example 915 MHz), the skin depth is 2.1 μm for silver, 2.2 μm for copper and 4.4 μm for brass.
To manufacture the antenna, a bare filiform core unwound from a storage reel is formed by plastically deforming it so as to give it a helical shape. The bare helical core is then coated with the brass coating. The coating step is carried out in an electrolysis bath.
As recalled above, for optimum operation of a brass-coated antenna at UHF frequencies, the thickness of the coating layer must not be less than 4 microns. Furthermore, because of the helical geometry of the core, the conditions for coating it are very difficult to control, especially inside the turns. Moreover, since it is made of an alloy, its precise composition is difficult to control and requires precise regulation of the parameters of the deposition process (currents, time through the bath, composition of the bath). To summarize, the quality of the deposit, together with the necessary thicknesses, results in a relatively long deposition time which has a major consequence on the cost aspect of the product.